Aladar pacz



' fication the particles of silicon containe Patented Mar. 8, 1932 UNITED STATES PATENT OFFICE ALADAR PAGZ, OF CLEVELAND, OHIO, ASSIGNOR TO ALUMINUM COMPANY AMERICA, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA TREATMENT OF ALU MINUM-SILIGON ALLOYS No Drawing. Application filed August 17, 1931, Serial No. 557,732, and

This invention relates to the modification of aluminum base alloys containing silicon.

The modification of aluminum base alloys containing substantial amounts of silicon is well known in the aluminum alloy art. The process generally consists in so treating the molten aluminum-silicon alloy that on soliditherein are present in the solid aluminum matrix in a fine and uniformly distributed form. Thus when aluminum-silicon alloys are. cast in sand, the silicon is present in the aluminum matrix in the form of large particles or needles, but if, prior to or during the casting operation, there is added to the molten metal ,a small amount of a modifying agent, such as an alkali metal, the silicon particles become much smaller in form an are usually rounded or oval rather than in the form of needles. While several means of modification have been proposed, a very successful procedure consists in the addition to molten aluminum base alloys containing silicon of an amount of an alkali metal, such as, fortinstance, sodium or potassium. The degree of modification obtained depends to a large degree upon the amount of alkali metal added to the molten metal, and attempts have therefore been made to introduce large amounts of alkali metal into molten aluminum alloys containing silicon. These attempts, however, have not been entirely successful in that the addition of large amounts of alkali metal to the molten aluminum-silicon alloys appears to lead to metal defects,

such as blisters and voids, and for this reason the addition of large amounts of alkali metals to the molten metal alloy has not been considered a successful or desirable expedient.

The object of the present invention is to provide a process whereby large amounts of alkali metal may be introduced into aluminum base alloys'containing silicon without the above-named disadvantages. The invention comprises applying to the exposed surface of the molten aluminum base alloy, prior to the time that the alkali metal is introduced, a salt covering or flux which substantially completely covers the entire exposed surface amounts of silicon,

in Austria December 28, 1930.

of the molten alloy, and thereafter introducing into the molten alloy and through the flux the desired quantity of alkali metal. By this process, it is possible to' add large amounts of alkali metal .to aluminum base alloys containing silicon without obtaining the injurious the double fluorides, the carbonates, and the effects heretofore obtained d when alkali metal was added in excess.

oxides of the alkali and alkaline earth metals,

and all such similar coatings which have d heretofore been used for the purpose of excluding air from the surface of the molten alloy or preventing oxidation or preventing dirt from' entering the metal. Although my invention is most useful and has the greatest effect when practiced in connection with aluminum base alloys containing very large I have found that excellent results may be obtainedwhen aluminum base alloys containing from about 3 to 35 per cent or more of silicon are treated in accordance with my invention.

The alkali metals which may be used in the practice of my invention include all of the metals commonly thus termed; that is to say, lithium, sodium, potassium, rubidium, and caesium. From the standpoint of operating expense, howeverfl prefer to use sodium and potassium since reasonable price and in commercial quantities. The amount of alkali metal which may be added to aluminum base alloys containing silicon in order to obtain a complete modification eflect varies, as is well known to the art, uponthe amount of silicon present in the alloy, the temperatures employed, the time at which the alloy is held at temperature before casting, and other known or obvious factors. But whereas the art has heretofore used amounts of alkali metal ranging from about 0.05 to 0.2 per cent of the total melt I have found that if the alkali metal is added to the molten alloy in the presence ofa cover-- they may be obtained at a ing salt, in accordance with my invention, amounts as large as 1 r cent may be added without deleterious e ect; and that the castings obtained are substantially freer of voids 5 and blisters and similar metal defects than could be obtained according to prior practices. a

- Having thus described my invention, what I claim is:

The process of modifying aluminum base alloys containing between about 3 and'35 per cent of silicon comprising covering the molten alloy with a salt flux and thereafter introducing through said flux and into said 15 molten alloy an alkali metal.

ALADAR PACZ. 

